Audio circuits to build

The following links to circuit diagrams and building projects I have found from other web sites. I have tested only very few of them so there is no guaratee that those circuit will work as expected. I don't have more info on those projects than what you can download from those sites which have the circuits. If you have more questions about those circuits then please mail the questions directly to the person who has designed the circuit or to the people responsible for those web pages.

Build a Class-A Amplifier
- This is an amplifier design made by Nelson Pass publishes at 1977. This amplifier gives out 20 watts per channel into 8 ohms, 24 watts into 6 ohms, and 28 watts into 4 ohms. The amplifier is powered from 120V AC power.
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"Quick and Dirty" Audio Amplifiers
- For those of you who like to experiment with audio circuits and would like a "quick and dirty" amplifier that frees you from having to figure out the biasing resistors, this article has two for you (and they run off 9 Volts too!). One uses an opamp and the other used a transistor.
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Vahvistin National Semiconductorin LM3886 piirill??
- Amplifier circuit which uses LM3886 IC. Text of this document is in Finnish. The article includes circuit diagram and circuit board design. The LM3886 is a high-performance audio power amplifier capable of delivering 68W of continuous average power to a 4Ohm load and 38W into 8Ohm with 0.1% THD+N from 20Hz-20kHz.
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Gainclone
- A LM3886 based Gainclone amplifier with input buffer and phase inverter for bridge connection. The LM3886 delivers around 68 watts and peak power of 120 watts.
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TDA7294
- The TDA7294 is a monolithic integrated circuit in Multiwatt15 package, intended for use as audio class AB amplifier in Hi-Fi field applications (Home Stereo, self powered loudspeakers,Topclass TV). This IC datasheet gives example circuit for up to 100W amplifier using this IC.
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The Class-A Amplifier Site
- Primarily dedicated to the John Linsley Hood Class-A amplifier designed in 1969 and updated in 1996. Copies of the original articles and additional design and construction information.
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Do It Yourself Car Amplifier
- This article is for those who wants to make their own car amplifier. The basics of calculation will be discussed below. If you have understand it you will be able to make car amplifier based on
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A DIY Headphone-Amplifier with Natural Crossfeed
- The in-head localization phenomenon of the headphones does not please many people. A "natural" crossfeed from the right (left) audio signal to the left (right) transducer, with an appropriate attenuation and delay, will reduce most of the adverse symptoms of headphone listening considerably.
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Ultra Simple Headphone Box
- Here is a very simple passive headphone box that works really good and can drive many headphones. You have to rely on the power of your power amp or your headphone out of your amp or your mixer headphone out to power it. Because there are no active components, there is very little that can go wrong with it and it is very quick to make. Because there are no potentiometers, you are not able to adjust the individual volumes of each headphone.
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100W Guitar Amplifier
- Guitar amplifiers are always an interesting challenge. The tone controls, gain and overload characteristics are very individual, and the ideal combination varies from one guitarist to the next, and from one guitar to the next. There is no amp that satisfies everyone's requirements, and this offering is not expected to be an exception. This amp is rated at 100W into a 4 Ohms load, as this is typical of a "combo" type amp with two 8 Ohm speakers in parallel.
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Historically, the job of a pre-amp was to boost incoming signal levels from your turntable or tuner to drive the the amp powering your speakers, and also to provide some switches and knobs for functions like volume control, source selection, and perhaps tone control. Nowadays you might sometimes see terms "passive preamplifier" or "passive linestage" and wonder what it means. Here is the description what they are: A passive linestage is an unpowered device typically located between the source components and the power amplifier/s. Because it is in the position which would otherwise be occupied by a preamplifier, and because it performs many of the same duties as a preamplifier, it is often referred to as a passive "preamp" although that term is not really accurate. Actually, the term "passive preamp" is slightly misleading. The word preamp or preamplifier is not supposed to be a passive device, as a passive device may not provide amplification. So a better term than passive preamp would be passive volume control or passive control center. The attenuator is enough for many uses, because with modern CD players and other sources providing sufficient output level to drive an amp to full output, a pre-amp doesn't necessarily need to provide gain anymore. Almost all modern audio source components (CD, DVD, tuner, DAT, etc.) will output a signal which is more than capable of driving a power amplifier. Volume control and source selection are still important, though. The passive preamplifier is a device that provides the gain control (variable attenuator controlled by potentiometer or switched resistor network) and source selection (set of switches). It may also include other features such as balance, muting, tape monitor selection, record out signal selection, channel switching, stereo/mono selection, channel reversing, headphone output, etc. Passive preamps have gained popularity in high-end audio circles. Provided that a high quality volume control is used, a passive preamp is often the easy and cheap way to reach high-end sound quality. Obvious advantage of parrive design is that there is no active or non-linear components no circuits, therefore no distortion! Unfortunately there tends to be a high output impedance and high capacitance.

Basic Passive Linestage
- A passive linestage is simple to build and makes an excellent first audio project. Building one is a good way to practice soldering skills and construction techniques, and as no power supply or active components are required it is also a safe project for beginners.
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An experimental RIAA preamp using no capacitors in the direct signal path
- The purpose of this report is to describe an experimental RIAA phono preamp that uses several different concepts to derive a high quality RIAA compensated phono preamp. Traditional RIAA compensation is done by way of resistors and capacitors to shape the frequency response. There are alternatives that use L-C-R networks to derive this compensation. In this preamp, we will use L-R only networks. The preamp uses unusual tubes.
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Get more power with a boosted triode
- Even though 6L6 beam-power tubes have been around for 66 years, they are still quite popular for use in electric-guitar amplifiers, and its cousin, the 6CA7 (EL34) power pentode, is a favorite among audiophiles. This design idea shows the 6L6 connected as a pentode, a true triode, and a "boosted triode," respectively. The boosted-triode configuration allows pentodes to produce pentodelike power while operating in a true-triode mode.
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Single capacitor powers audio mixer
- micropower and low-voltage op amps allow you to build high-performance analog-signal processors that require no batteries or wall transformers, this simple mixer is powered using one large capacitor such as a Supercap or Dynacap for some time
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Simple Line Mixer and Patchbay
- Make a simple line mixer to run the sound modules through in the studio. This mixer as simple as possible because of the time factor, and also to avoid unnecessary noise that a more complex design could create. It consists of 5 stereo inputs to plug in 5 stereo sound modules and a stereo out with volume controls.
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DI-box is an electronic device for helping to interface electronic music instruments (like electric guitar and syntetizer) to mixing desks. DI boxes are used to connect instruments, e.g.bass, keyboards, directly to the console, i.e. without using a microphone. They can be passive (containing no powered electronics) or active (with powered electronics) and they are usually fitted with ground lift and pad switches. DI-box is designed to transfer the sound of your instrument to the mixing console, adding nothing and taking away nothing. The function of DI box is to convert an unbalanced, high impedence source, to abalanced, low impedence source for improved noise immunity and toavoid degradation from long (more than few meters) cable runs.The output of the DI box is connected to the balanced microphoneinput of the mixing desk. One of the most important things a DI has to do is create a balanced signal from anunbalanced signal. Typical terms you will see are "transformer balanced" and"actively balanced." The result is a balanced, low impedance sendthat can travel down a snake without coupling all manner of noise on aline or instrument level signal. Typical keyboard or other musical instrumentsuplies a low impedance, but unbalanced output (which is prone to pick upnoise on long runs).Generally DI box takes an unbalanced input and (withvarying amounts of isolation depending upon the box) provides a balancedline. It may also provide other functions - ground lifts, gain pad, etc.Many DI boxes provide also ground isolationwhich helps you to get rid of humming caused by ground loops(Hum and buzz are often caused by a connection between the mixer and ground at the guitar system.)DI-box can be used as a "splitter" when you plug (say) a guitar pickupin one 1/4" unbalanced jack and 1 /4" unbalanced patch to the guitar ampinto the other.

A mic preamp boosts the very sensitive low level (millivolts) audio signal from a microphone to a more usable level, called "line level" (typicaly from 0.1V to few volts). The mic level signal can easily be degraded by cable length, cable capacitance, and other such things. A line level signal is vastly more robust, and is the levelused to ship audio around from consoles, toprocessing equipment, to recorders or amplifiers.Typical microphone preamplifier needs to produce around 40-60 Db of gain(what is needed depends on microphone and sound level). Usually microphone preaplifiers have gain adjust option in them.

DIY Speaker Testing Microphone
- One problem most people have when starting to test their speakers using computer-based testing software and hardware is the mic. The mic is arguably the most important piece of the process, but the availability of high-quality, commercial mics with relatively flat response from at least 20hz to 20khz is low and those that are available are quite expensive. The whole process for building this mic yourself should take under an hour, but you'll need a few things.
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Low impedance microphone amplifier
- The circuit is a microphone amplifier for use with low impedance (~200 ohm) microphones. It will work with stabilized voltages between 6-30VDC. This circuit can be also adapted for higher impedance microphones (instructions for this are given).
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Portable Microphone Preamplifier
- This circuit is mainly intended to provide common home stereo amplifiers with a microphone input. This 9V battery powered amplifier circuit is based on a low noise, high gain two stage PNP and NPN transistor amplifier, using DC negative feedback.
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Preamp for low-Z microphones
- This is a low input impedance, high quality pre-amplifier of the sort that could be used in a stage mixing desk. This circuit is built using diescrete transistors and uses a dual rail power supply.
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Build a Microphone plug
- You only need a 3.5 mm plug (mono) and a very small microphone which is soldered directly onto the contacts of the plug and fits in its housing to build this small microphone for Zaurus palmtop computer.
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Microphone uses phantom power
- Phantom-powered microphones derive power for their active circuitry from the receiving-end circuit through the same leads that transmit the audio signal. This design uses this "phantom power" for the electret microphone capsule and a small preamplifier fitted inside microphone.
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Furious contact microphone assembly
- This is one way to put together a contact microphone. It is not the best way, but the end result is pretty satisfying and it doesn't cost much (once you have a soldering iron). The functional element is a piezo electric transducer.
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So, you want to build a pair of binaural microphones?
- Small binaural microphone pairs are popular for unobtrusively recording musical and other events. A number of people sell ready-made sets and many of them are based on the Panasonic omnidirectional electret mic capsule, which sells for around $2 a capsule, and the other associated parts and electronics bring the cost of a set of home-brew binaurals to about $20, far less than the price of a set from commercial manufacturers.
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How to build a microphone
- For decades condenser microphones have been the staple for high-quality recording and live sound assignments. Unfortunately, not everyone can afford to own a good one. Well that?s about to change. This article has been written so that anyone who wants a great condenser mic (or those who just want more of them) can have their wish. For around $20 (US) anyone can build an extremely accurate, life-like condenser microphone.
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Pop free Microphone on/off switch
- This circuit uses a simple technique to eliminate the usual "pop" sound when an electret type microphone is switched on or off. The circuit is completely passive and will work on dynamic and electret type microphones.
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A phono preamplifer is a device which converts the electricalsignal from phono player to a line level signal.The output of a record player is muchlower (few mV) than a line-output signal, and needs to befrequency-corrected (RIAA-correction) and amplified to makeit usable as other line level signal sources.A typical phono input has an EQ curve (RIAA) sloping over 40dB fromlow to high frequency. It also expects an input of ~3.0 millivolts @1KHz. If your stereo amplifier does not have an input for a record player, you should use a phono preamplifier circuit between your turntable and your amplifier. The output of your turntable follows a gain-bandwidth curve called the RIAA compensation curve. The standard AUX input on your stereo does not. Records will sound very strange without an RIAA preamp.

Audio level control with resistive optocouplers
- Controlling the level of an audio signal by means of an applied voltage or current has always been somewhat problematical but often desirable. . This application note deals with voltage or current controlled attenuators using optocouplers, primarily in relatively static situations.
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Audio switching applications for resistive optocouplers
- Electronically switching audio signals can be a more complex matter than it might first appear. Not only are there the obvious problems of interfacing between your control logic which is running off a 5V supply and something that is probably controlling a larger voltage swing, but there are the various imperfections of the switch element to consider, which can degrade your precious audio signal.
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CMOS IC makes low-cost digital potentiometer
- A growing trend in the design of electronic equipment is to replace analog knobs used to increase or reduce a continuous signal (such as volume or brightness) with "up" and "down" keys. However, replacing a low-cost analog potentiometer with a digital potentiometer can be costly. The low-cost circuit presented in this article can eliminate the analog potentiometer in many applications. The circuit is based on a 16-channel CMOS multiplexer/demultiplexer and a string of resistors.
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Convert voltage to potentiometer-wiper setting
- This circuit converts an analog input voltage, VIN, to a proportional wiper setting of a DPP (digitally programmable potentiometer). The potentiometer's wiper setting, which varies from position 0 through 31, corresponds to the input voltage, which varies from 0 to 1V dc. Thedigital potentiometer used is CAT5114, a 32-tap potentiometer with an increment/decrement interface.
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Fixed Attenuators
- Fixed attenuators can be designed to have either equal or unequal impedances and to provide any amount of attenuation (theoretically) equal to or greater than the configuration's minimum attenuation - depending on the ratio of Z1/Z2. Attenuators with equal terminations have a minimum attenuation of 0 dB. Unequal terminations place a lower limit on the attenuation.
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Gain Control
- Applications as disparate as test equipment, audio, medical imaging, and cellular base-station radios need to manage signal amplitudes in the analog domain. This article tells about those applications.
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Improve FET-based gain control
- One problem with standard FET gain-control circuits is increased noise when you use the FET as a part of a resistive attenuator in series with an op amp. When you substitute the FET for the gain-setting resistor in a noninverting op-amp circuit, distortion limits the circuit configuration to applications in which the input voltage is less than a few hundred millivolts.
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Linear potentiometer implements logarithmic gain control
- Trimmer potentiometers are ubiquitous components and are available in a variety of packages, resolutions, and temperature stabilities but none of these potentiometers implements anything but the usual linear function of resistance vs shaft position as useful in many audio applications. This fact makes trouble for applications that need a wide dynamic-adjustment range. Fortunately, you can use a circuit that approximates a logarithmic gain control using a standard linear-taper potentiometer. By using the wiper as an input terminal, you can use a standard linear-taper potentiometer to implement logarithmic gain control.
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Op amp linearizes attenuator control response
- Professional-audio equipment commonly uses Analog Devices' (www.analog.com) high-performance, quad-voltage-controlled SSM2164 attenuator. The control response is -30 dB/V, with 0V producing unity gain. Attenuation increases as the applied control voltage increases in the positive direction. This circuit extends the range of applications for this versatile chip by providing a simple means of linearizing the control response. The result is an amplifier with gain directly proportional to the control voltage.
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Op amp linearizes response of FET VCA
- FETs find common use in VCAs (voltage-controlled amplifiers) and attenuators, in which the FET serves as a variable resistance. A control voltage applied to the gate sets the channel resistance and overall circuit gain. You frequently need to select individual FETs because of wide spreads in FET characteristics. This circuit uses a master-slave servo technique with a matched-FET pair to implement voltage-controlled variable gain. In this circuit the gain increases linearly from -55 to 0 dB as control voltage varies from 0 to 5V.
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Printer port activates CMOS switches
- This cost-effective design provides control for CMOS switches without the need for an external power supply. Analog switches such as those in the MAX4663 are ideal for use in low-distortion applications. They are preferable to electromechanical relays in automatic test equipment or other applications in which you need current switching. The CMOS switches use lower power, consume less board space, and are more reliable than electromechanical relays.
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Single switch controls digital potentiometer
- The control of electronic potentiometers in most today's applications comes from controller-generated signals. However, a significant number of applications exist that require adjustments using manual, front-panel controls. This circuit uses one IC, one switch, and 10 discrete components. It implements the interface of a single DPDT, momentary-contact rocker switch to a DPP (digitally programmable potentiometer) that has a three-wire increment/decrement interface.
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Single switch controls digital potentiometer
- This Design Idea is an evolution and simplification of another. As the earlier design also describes, you can activate the DPDT rocker switch, S1, to produce either a "count-up" or a "countdown" effect at the digital potentiometer, CAT5114.
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Technical Secrets of the Crossfader
- A crossfader is designed to predictably control the outputs of two separate mixer channels based on the relative position of the fader's knob between its endpoints. It's a simple sounding task but there are many different ways the job can be done, electrically and mechanically. This document describes some of the most commonly used ones. Most crossfader circuits are implemented in one of two basic schemes.
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Variable-gain stage uses voltage-output DAC
- A voltage-output DAC normally generates an output voltage that is a fraction of the input-reference voltage. In many designs, however, it is necessary to multiply the input voltage by a programmable gain, or, in other words, to create a variable-gain stage. You can easily implement a variable-gain stage using a low-cost voltage-output DAC and one operational amplifier. This no-buffer design minimizes noise and voltage offset, but you can use buffered DACs, too. An 80C51 ?C controls the DAC using a three-wire-plus-reset interface.
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MOSFETs reduce crosstalk effects on analog switches
- Some cost-effective analog multiplexer/demultiplexer ICs, such as the CD4053 and CD4066, find frequent use as signal distributors. These digitally controlled analog switches have low on-resistance. However, with all channels in the same package, crosstalk can be annoying and unavoidable. The circuit presented in this article provides a cost-effective and viable method of solving this problem.
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Passive filters fill the bill at audio frequencies
- Low-frequency filters, particularly at audio frequencies, usually take the form of active filters. These filters eliminate expensive inductors with windings of many turns. However, passive filters remain a viable option when you quickly need low-cost prototypes and test pieces.
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Subwoofer Equaliser Using The Linkwitz Transform Circuit
- The Linkwitz transform circuit is a hugely flexible way to equalise the bottom end of a sealed loudspeaker enclosure. A speaker that is corrected using this method is flat from below resonance to the upper limit of the selected driver. The low frequency rolloff point is determined by the parameters of the transform circuit. Should the enclosure size be too small and cause a lump in the response before rolloff, this is also corrected. A conventional active crossover network is then used to divide the subwoofer signal from the main channel signals. Note that there is also a separate
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A crossover is a device designed to divide audio information into smaller frequency ranges to comply with the requirements of different transducers in an audio reproduction system. This is accomplished by running the audio through a set of filters. Crossovers can be passive or active designs. Passive crossovers are usually found inside speaker cabinets along with the speaker components. These often connect to the outside world via a single jack, but sometimes each speaker component also has its own jack in case one wants to bypass the built in passive crossover. Active crossovers are placed before the power amp. In that application each frequency range is given its own power amp and its own drivers.

Passive filters fill the bill at audio frequencies
- Low-frequency filters, particularly at audio frequencies, usually take the form of active filters. These filters eliminate expensive inductors with windings of many turns. However, passive filters remain a viable option when you quickly need low-cost prototypes and test pieces.
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An audio compressor serves to reduce (or compress) the dynamic range of the input signal, keeping the level more constant, so that it may be more clearly heard above background sounds, whether they be noise or accompanying musical sounds. An ideal compressor introduces little distortion and noise when it is inactive, and controls the audio level in a way that is pleasing to the listeners ear.> An audio limiter serves to prevent the signal level from exceeding a preset limit, and as such is often used to protect a following device from overload. These can include recorders (both analog and digital), transmitters and power amplifier / loudspeaker combinations. An ideal limiter introduces very little distortion or noise when it is inactive, and controls the audio level in a way that is pleasing to the listener's ear, while keeping tight control over the output level.

Designing A Limiter For Headphone Amplifiers
- When used with headphones - especially personal monitors, audio limiters (also called clippers) can help maintain safe listening levels. Without a limiter, large transients in audio signals could generate dangerous SPLs in headphones, although the average volume might be set at an acceptable level. Because a limiter is actually a specialized form of audio compressor, the circuitry of audio limiters can vary tremendously in complexity from a pair of diodes to multi-stage voltage controlled amplifiers with split frequency bands. Diode-based limiters are instanteous, simpler in design and have a more accurate loudness response, but suffer from distortion in the clipping region.
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Dynamic Range Processor
- this stereo unit allows the dynamic range of a signal to be increased (expansion) or decreased (compression) by a variable amount up to 3:1, based on the SSM2120 dynamic range processor IC
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Electric guitars use usually stronger in voltage than a microphone and yet lower than a line-level signal.Typical voltages for these signals are roughly 1 volt for line level signals, and maybe 100 millivolts for a microphone (depends on the microphone type). The voltage off an electromagnetic guitar pickup can be a healthy 2.0 Volts or so peak-to-peak if you're playing hard. The impedance of that signal varies greatly over the frequency spectrum and a high impedance signal can be damaged interfacing to the outside world. The load capacitance of a guitar cord can attenuate the high frequencies and lower the tuning of the resonant peak of the pickup.
When selecting the cable from guitar to amplifier the important thigns to consider are the big issues are the capacitive loading of the inductive pickup, how wel the cable is shielded and hot well it can take the hard stage use (both connector and cable material quality).
The guitar cords are typically 10-15 feet long, longer cables can be sometimes used. It's not like there is a length where it's suddenly too long. Whether recording or otherwise performing, the answer is when your ears tell you that the cable length is resulting in unacceptible high frequency loss or other sound quality problem.

The input impedance of a guitar amp, mixer or effects boxes can attenuate or distort parts of the guitar signal. And because the guitar signal is not very robust, external noise sources and grounding can become serious problems. The guitar's volume control further increases the output impedance, multiplying the problems. A preamp can address these problems by acting as a buffer, providing the guitar pickup with an optimal high impedance load and driving the cable, effects boxes, and amplifier with a robust signal. Most guitars do not have preamplifiers in them. The input impedance of a proper guitar amplifier is high, usually in order of hundreds of kilo-ohms. Some sources even say that 1.0M ohm is the minimal acceptable input impedance for a guitar device. Electric guitars are generally know to pick up electrical noise easily. The reason for this is typically that the system is high impedance (noise gets easily through cable if not very well shielded) and the magnetic pickup system can pick up external magnetic field (for example from nearby transformer). If your electric guitar is picking up lots of noise, then first check that the cable is in good condition and constructed well from goof materials. If this is not the problem, then it is possible that the pickup is badly designed, or ungrounded, or unshielded, or needs to have an unbalanced-to-balanced transformer.

When you need to get the guitar signal long distance from the guitar amplifier to PA system, you need a proper DI box to do the job.
An active direct box would probably help the most. A good transformer-based direct box can buy you a lot.

A D.I.Y. Guitar Effects Prototyping Board
- A versatile DIY Guitar Effects Prototyping Board. The best way to experiment is by using a "breadboard". A breadboard is simply just some molded plastic with a series of openings 1/10" apart, connected in rows by metal clips on the underside of the breadboard. Since guitar effects circuits all have some things in common, such as input and output jacks, volume and/or gain controls, tone controls, etc., you can permanently mount the breadboard, some spare pots and jacks to a piece of wood and hard wire them to the breadboard. Also links to guitar stompbox circuits, guitar amps and other useful information related to electric guitar.
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FET Preamp Cable
- Preamp Cable is a phantom powered discrete FET (Field Effect Transistor) preamp built into the plug of a guitar cable. It provides almost all the advantages of an on-board preamp.
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Guitar Amplifiers
- Guitar amplification is a specialised field, where much commonly understood theory does not apply, and little theory is published. Technically speaking, a guitar amplifier has a specific type of non-linear gain at its signal extremes, and a specialised type of limited frequency response. This article collection has lots of information on guitar amplifiers.
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The Technology of the Tube Screamer
- The Tube Screamer series of distortion/overdrive boxes from Ibanez has a reputation that has led them to pass into musical urban myth. Helped along with Stevie Ray's use of them, the TS 808 and TS 9 have been sought after and traded up to astronomical prices. All the members of the TS family share a common technical design, with the similarities vastly overwhelming the differences. This document describes the technologies used in them.
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The Technology of Wah Pedals
- The stock "wah" pedal has been around since at least the early 60's. This thing produces a distinctive tone that is well loved by the expressive guitarist. What a wah does is clear - it is either a bandpass filter or an overcoupled lowpass filter that exhibits a resonant peak just at its lowpass rolloff frequency. The resonant peak can be moved up and down in frequency by the player, and this makes for a striking emulation of the human voice making a "waaaah" tone, or its tonal inverse, "aaaooow".
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Philips' Dynamic Noise Limiter
- This four transistor circuit is claimed to be developed by Philips to improve the subjective signal-to-noise ratio of cassette reproduction. It works on playback only and therefore can be used with any source material. Indeed, it can improve the sound of not only tape playback but any source where broadband noise (hiss) is troublesome - noisy radio signals are examples.
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Digitally Control Phase Shift
- Altering the phase response of a signal without changing its amplitude characteristics is commonly performed using an allpass filter. This circuit implementation is well suited to using digital potentiometers as the controlling element.
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S/PDIF

NOTE: The digital output of a typival PC CD-ROM is generally at TTLlevels, roughly 0 and 5 volts. This is different from SP/DIF standards, which are +/- about half a volt. However, many SP/DIF inputs include means for eliminating themismatch in DC levels and they can also easily withstand the extravoltage.

DAC

Signal conversion

Equipment modifications

Common AC-3 RF Circuit Designs
- The following circuits are three popular AC-3 buffer designs used in most laserdisc players currently on the market. Since all the designs are simple variations of an emitter-follower, these circuits act as current buffers with the ability to change the DC level for muting.
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The d-box in a better look
- Everything described here relates to the Mediamaster?? 9200, 9500 and 9600 as well as to the d-box?? available until december 1999. This page described how to add S/P-DIF Output to this DTV box.
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Simple circuit forms peak/clipping indicator
- This simple peak detector is the result of a need for a single-5V-supply, level/clipping indicator for a multimedia-PC sound system. The design is unique in that it detects both stereo channels on a single peak-hold capacitor. All the adjustments in the circuit simultaneously apply to both left and right stereo inputs. The output is suitable for driving a bar-graph display or for analog-to-digital conversion and display with a microprocessor. The circuit operates as a dual positive-peak-detector circuit.
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Stereo VU Meter
- This is a very eye appealing audio accessory. Displays an approximate output level for each channel of a stereo amplifier. Connects to the speaker terminal; levels are displayed in ten steps. User may select either a moving dot bar appearance. Uses two LM3915 IC's; includes a discussion of measuring audio power.
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Decibel meters

Filters needed in audio mesurements

The problem of measuring audibility of sounds is complicated by the nonlinearity of human hearing. The frequency dependence of human hearing is described by the Fletcher-Munson Curves. The Fletcher-Munson Curve explains the non-linear response of the human ear ensitivity to pure tones, but in practice, many sound sources are anything but pure. The apparent loudness of a frequency mix is not necessarily a simple combination of responses to individual frequency bands.Owing to the complexity of operation of the human ear, it is not possible at present to design an objective noise measuring apparatus to give results which are absolutely comparable, for all types of noise, with those obtained by subjective methods.In an attempt to account for human hearing sensitivity in a standardized way so that measurement instruments can be compared, the International Electrotechnical Commission (IEC) issued Standard IEC 651 (1979). This standard identifies four application types (types 0 through 3) and three weighting curve characteristics (A, B and C). Historically, the A, B, and C weighting networks on a sound level meter were derived as the inverse of the 40, 70 and 100 dB Fletcher-Munson curves and used to determine sound level. The lowest curve repesents the threshold of hearing, the highest the threshold of pain.The A-weighting characteristic is most widely used, and though originally intended for low-level sounds, it is commonly applied to higher sound levels as well.

Testers

ABX Double Blind Audio Tester
- This project describes the construction of test equipment for double-blind or ABX testing of source components - preamplifiers, tuners, DACs etc. or even, if that is your particular vice, interconnects. Double-blind and ABX tests do not allow the listener to know which component they are listening to, and furthermore don't allow the test controller to know either. This guards against visual cues to the audience (including body language).
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Distortion measurements

Distortion Analyser
- Total harmonic distortion (THD) measurements are one of the most commonly quoted in audio. Contrary to belief in some circles, these can be very useful if performed properly, and reveal much about the overall performance of an amplifier. There are a number of ways to measure distortion, none of which is perfect. The standard tool for measuring THD is a notch filter. This is tuned to reject the fundamental frequency, and any signal that gets through is a combination of the amplifier's noise (including any hum) and the distortion.
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Power Amplifier Clipping Indicator
- At some stage, we will all find ourselves pushing hi-fi equipment just a little too hard, and if lucky, will just find that the sound has become "dirty". If this happens too often or is too severe, tweeters are the first to go - they are damaged by the excessive power generated by a combination of "power compression" and the harmonics created when an amplifier clips. What is needed is a simple and reliable way of detecting that the amplifier is clipping (or so close that we have no margin for error). Well, search no more, because here it is.
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Other measuring circuits and notes

3 Channel Spectrum Analyzer
- This 3 channel 15 LED spectrum analyzer can be used as an addition to any audio amp project. It produces fantastic displays on three LED bars that can be individually adjusted for any particular frequency range.
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Infrared Head Phones
- Using this low-cost project one can reproduce audio from TV without disturbing others. In place of a pair of wires, it uses invisible infrared light to transmit audio signals from TV to headphones.
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Circuit combines power supply and audio amplifier
- This circuit can helpful if you must transfer dc power and audio over a pair of copper wires. The circuit uses only one IC, the well-known LM317, a low-cost power-supply regulator. Using this chip, you can modulate the adjustment-pin input with the audio signal from an electret condenser microphone, connected between the output and the adjustment terminals of the IC.
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EDN ears-on project: Listening to Class D
- You needn't look further than Class D audio amplifiers to find a technology whose proponents tend toward exuberant advocacy at best and bald-faced hype at worst. Although these ICs are not yet the be all and end all of audio amplification that their makers would have you believe, they are remarkably good-certainly more listenable than the clamor about them.
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Mains voltage filter and isolator
- A good clean voltage source for your stereo does help with the sound quality. This is a simple power line conditioner. There are three outputs. The first output is an isolated one which will be used for noisy products like cd players.The second output is through a low pass filter(20KHZ),for products like turntables. The third is a straight through with no filter,for high current products like amplifiers.
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